TAGIII, I would suggest a letter. I don't know if you've had the opportunity (given the short amount of time that you get to be home) to talk to her. When NOP and I work battling our way through our issues, writing help tremendously.
A letter is so much more personal than flowers or cards. Perhaps a listing of "you mean so much to me because"? or a listing of highlights of happy times in the 30+ years you've been together?
The first time you met. When you realized you were in love with her. The marriage proposal. The birth of your children. Special holidays or vacations. Hard times when she provided strength or solace to you.
Kind of a "remember when" collage geared toward expressing your love for her and tender memories of good times together.
Of course, weigh the suggestion with what you know about your wife. Some folks feel that flowers and cards are a necessity for holidays and to fail to provide them would be disappointing.
I know that when NOP and I discuss our almost 30 year history, we have milestones that we can look back on. The remembering of which draws us together emotionally & mentally because of those bonds that we've shared.